覆盖printf方法

Question

I want to create a function that will work exactly like fmt.Printf but also left pad the string with current timestamp. Ideally I would like to override printf and println to do this job, but the first solution is also ok.

This is what I've done:

func output(message string, a ...interface{}) {
    fmt.Printf(getCurrentTime() + " " + message, a)
}

func getCurrentTime() string {
    t := time.Now()
    return t.Format("[2006-01-02 15:04:05]")
}

But it outputs strange results when I pass variables.

How should I do this?

Answer 1

If you want to pass variadic elements from a function to another, you have to expand them. From your example, a is an []interface, so you are passing only two arguments to the actual fmt.Printf: the message and an array.

You have to correct the call:

fmt.Printf(getCurrentTime() + " " + message, a...)

A little example to show what happens:

func exec(args ...interface{}) {
    fmt.Println(args)
}

func insert(args ...interface{}) {
    exec(args)      // Prints [[5 42]]
    exec(args...)   // Prints [5 42]
}

func main() {
    insert(5, "42")
}